In the fields of art supplies, textiles, and chemistry more generally, the principle of leuco dyes—dyes that can be induced to transition between a first, white or colorless “leuco” form and a second, colored form—are well known. Leuco dyes may be induced to transition in response to a change in temperature, exposure to ultraviolet radiation or other light, and/or exposure to a chemical, such as an acid, a base, or even oxygen in the atmosphere.
Although a leuco dye may be used in a water-based marker, such markers have the drawbacks of potentially leaking or drying out over time and becoming unusable. Further, if such a marker is used on an ordinary surface such as a sheet of paper in a notebook, reaction with ambient heat, light, or air may take a substantial period of time to trigger the visible transformation of the dye, leaving a user of the marker unsure whether the marker is working, or frustrated at the delay in the appearance of color on the page.
Additionally, water-based activators for leuco dyes are often limited in applicability due to the lower viscosity or other chemical properties of the activator. For example, a printer might be unable to print activator-based ink only on portions of a sheet of paper, and the only feasible way of adding activator might be dipping or coating the entire surface in activator.
Some existing methods of storing leuco dye or its activator in preparation for applying it to a surface involve encapsulating the leuco dye particles or activator in protective spheres such that, when the leuco dye is mechanically pressed against the activator, the spheres rupture, allowing the leuco dye and activator to mix freely, and transition to a colored form. However, encapsulation is an expensive process, and the capsules may be ruptured by rough handling either during manufacture or by the end user, ruining and losing the encapsulated dye before it gets to the activator. Thus, an encapsulating process is forced to thread a needle between being hard enough to survive a manufacturing or printing